The Earth's magnetic field can assist in finding a direction or bearing to any object or location by using a magnetic compass. In a traditional magnetic compass, a magnetic needle or card detects the magnetic field lines of the Earth and always points in a direction toward magnetic north such that a compass bearing or direction can then be calculated. Additionally, the resultant compass readings can be presented on a digital display which show the bearing to an object or the heading of a boat, aircraft or vehicle. Therefore, by knowing the direction of magnetic north, it is possible to compute the bearing or direction toward any given object or location.
However, magnetic north is not the same as true north since the magnetic north pole is not positioned concentrically with the North Pole of the Earth. Therefore, the compass needle will point in a direction along a curve leading to the magnetic north of the Earth and not toward the North Pole. Additionally, the Earth's magnetic field slowly moves monotonically over time thereby causing a time-based deviation between magnetic north and true north as well.
Surveys of the magnetic field lines of the Earth have been made which show the deviation between magnetic north and true north in degrees. It has been found that in some locations of the United States, there can be as much as 23 degrees of deviation between what a compass reads as magnetic north and the direction to true north. Therefore, as an aid in calculating a bearing based upon true north, maps and tables have been created which catalog and chart the deviation between magnetic north and true north for any location, as well as show the deviation based upon time. As such, in a given location, it is possible to find true north by correcting a magnetic compass reading by the amount of deviation for that present location at the present time and then correspondingly correcting all magnetic bearings to true bearings.
Bearings based upon true north are invaluable for navigators and mappers. As previously described, the deviation between magnetic north and true north varies by location. Therefore, in a fast moving aircraft, a magnetic compass cannot give accurate directional information to a navigator or pilot because the magnetic compass readings change as the aircraft changes location. As such, presently aircraft use gyro-compasses that are able to display true north readings. However, gyro-compasses are expensive and bulky and are not suitable for all applications.
Additionally, bearings based upon true north are easier to use on maps and charts. Since most charts are oriented by latitude and longitude lines that are based upon true north, it is easier to find locations on a chart knowing a true bearing. Additionally, map makers need to use true bearings when making a large map over a wide-ranging area because the magnetic bearings can vary significantly between location. Therefore, there is a need for an affordable and compact compass that reads true bearings.
The present invention addresses the deficiencies in the prior art magnetic compasses by providing a system that presents true bearings in a compact and inexpensive unit. Additionally, the present invention can compensate for time-based deviations of the Earth's magnetic field. Finally, the present invention can provide a system that displays a true bearing, a magnetic bearing and a present location in a single unit.